Virtually every animal on Earth interacts with bacteria. In many cases, over the course of ancient symbioses bacteria have evolved specific small molecule natural products to interact with their host organisms and with other competing microbes. These compounds can be exceptionally bioactive, and some are even FDA-approved agents for treating diseases such as cancers. The molecules presumably co-evolved with their molecular targets in many different animals, meaning that they are selected by evolution to have functional effects on animals. In turn, these effects can be exploited for the creation of new pharmaceuticals. These interactions are just beginning to be understood and represent a virtually untapped reservoir for discovering agents with potential to treat human diseases. Here, we will perform fundamental experiments on marine symbiotic systems, cultivate bacteria, and discover and develop bioactive small molecules. Our focus will be on molecules that affect competing bacteria (antibiotics) and the host organism (molecules that affect eukaryotic cells and might have use in neurology or oncology). We will take a rational, hypothesis-driven approach to understanding and exploiting symbiotic interactions. In this proposal, we will focus on associations between animals and bacteria in US coastal waters. There, we have found specific symbiotic bacteria that synthesize unexpectedly diverse new, bioactive compounds. We seek to understand these interactions while obtaining new compounds for further development as therapeutic agents. Our aims are to: 1) Understand how natural products shape symbiotic interactions. We will focus on specific interactions between different phyla of marine invertebrates and their associated, cultivable bacteria. 2) Discover new natural products from cultivated bacteria. We will use a metabolomics approach to rapidly hone in on previously unknown natural products. These compounds have been proven so far to be exceptionally active and include new compounds with new carbon skeletons. We will focus on innovative antibiotic and neuroactivity assays available at University of Wisconsin and University of Utah. We will also develop libraries that can be more widely screened. 3) Develop natural products for application in treating human diseases. We will combine chemical and biotechnological approaches to assess the promise of newly discovered agents and to move them toward application. We will begin with a few lead compounds already discovered in our labs, then use the established pipeline for other agents discovered in this project.